Multi-post Structures for MEMS Fusion Bonding
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Solution Overview
Problem
Existing semiconductor processing techniques for MEMS devices face challenges in forming complex multilayer structures with precise features without introducing additional layers or damaging the substrates, particularly in achieving a stable and permanent bond between substrates while allowing for precise etching and feature formation.
Innovation Solution
The method involves fusion bonding of silicon substrates without an intermediate layer, using deep reactive ion etching to create post structures, and separating the substrates to form a monolithic structure with precisely defined features, allowing for the formation of complex 3D geometries and multilayer structures without additional material layers or damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If fusion bonding is used to bond substrates without a bonding layer, then the bond stability is improved, but oxide formation between layers occurs
Solution Approach 1:
The substrates undergo preliminary cleaning and oxide removal treatments before bonding to prevent oxide formation. The bonding process is initiated immediately after surface preparation to ensure direct substrate contact without oxide interference, thus achieving stable bonds without the harmful oxide layer formation.
Solution Approach 2:
The bonding process is conducted in an inert atmosphere or vacuum environment that prevents oxidation of the substrate surfaces. This controlled environment eliminates oxygen exposure during the critical bonding phase, allowing stable fusion bonds to form without oxide contamination between layers.
2Manufacturing precision
If deep reactive ion etching is used to create precise post structures, then the manufacturing precision is improved, but the substrate profile is altered
Solution Approach 1:
The etching process is applied selectively to specific regions of the substrate where post structures are required, while other regions maintain their original profile. Masking techniques are used to confine the etching action to precise locations, achieving high manufacturing precision for posts without altering the overall substrate profile in non-target areas.
Solution Approach 2:
The etching process removes only the necessary amount of material to create the post structures with precise dimensions. By controlling etch depth and duration to match the exact requirements, the substrate profile is modified minimally only where needed, preserving the overall substrate shape while achieving precise post formation.
3Device complexity
If substrates are separated after bonding to form unitary structures, then the device complexity is reduced, but the bonding permanence is compromised
Solution Approach 1:
The fabrication process is segmented into distinct phases: temporary bonding for alignment and feature formation, followed by controlled separation, and finally permanent bonding to create the unitary structure. This segmentation allows substrates to be temporarily joined for processing, then permanently integrated into a single structure with all desired features, reducing device complexity while maintaining bond permanence in the final product.
Solution Approach 2:
Substrates are preliminarily bonded together to perform alignment and feature formation operations before final permanent bonding. This preliminary bonding enables precise positioning and feature creation, after which the structure is separated and re-bonded permanently, achieving both the reduced complexity of a unitary structure and the permanence of stable bonding in the final device.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables the creation of micromechanical devices with precise features and stable, permanent bonds, preventing oxide formation between layers and maintaining the substrate profile during etching, thus facilitating the production of complex multilayer structures with improved precision and structural integrity.
Implementation Method 1
Two silicon substrates can be fusion bonded together
Implementation Method 2
The assembly can be annealed so that the first substrate and the structures become permanently bonded together
Implementation Method 3
The patterning can be done by deep reactive ion etching
Data Source
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AI summary
Micromechanical devices having complex multilayer structures and techniques for forming the devices are described.